The present invention is directed to a modified polyolefin, a procedure for the manufacturing thereof, and to the use of the modified polyolefin. More particularly, the present invention is directed to manufacturing an olefin/vinyl alcohol block copolymer.
Ethylene/vinyl alcohol copolymers are presently being manufactured by hydrolyzing an ethylene/vinyl acetate random copolymer. Hydrolysis (alcoholysis) is effected with the aid of an alcohol. The mixture may be either acidic or basic. Hydrolyzing may be carried out in a solid state, in a molten state, or in solution. These ethylene/vinyl alcohol copolymers are random copolymers.
There is a number of patents concerning this procedure for manufacturing the ethylene/vinyl alcohol random copolymer, a summary of which is found in the article "Reactivity of Ethylene Vinyl Acetate Copolymers: A Critical Evaluation of the Comprehensive Patent Literature on the Acetoxy-Hydroxide Transformation of Ethylene Vinyl Acetate Copolymers", by R. J. Koopmas, R. van der Linden and E. F. Vansant, in Polymer Engineering and Science, July 1982, Vol. 22, No. 10, Page 645. All these procedures are based upon hydrolysis of the acetate group to become an alcohol group; there is no mention of any block copolymers.
Commercial ethylene/vinyl alcohol random copolymers are of two types. Grades containing 20 to 30 mol-% vinyl alcohol are being marketed, for use principally in extrusion and in powder coating of steel tubing ("Levasint" by Bayer, and "Mirawithen" by VEB Leuna-Werke Walter Ulbricht). These brands are made from ethylene/vinyl acetate random copolymer manufactured by a high pressure technique.
Additionally, commercially available grades contain 60 to 80 mol-% vinyl alcohol, which are mostly used for gas-barrier layers in multi-layer products (EVAL by Kuraray, and Soarnol by Nippon Gohsei). These grades are manufactured by adding ethylene to the polyvinyl acetate process, and hydrolyzing the product in the same manner in which polyvinyl alcohol (PVA) is made from polyvinyl acetate. The gas-barrier of the product drops abruptly if there is less than 60 mol-% vinyl alcohol.
When the ethylene/vinyl alcohol random copolymer contains more than 60 mol-% vinyl alcohol, it forms monoclinic crystals (the same as PVA); when there is less than 20 mol-% vinyl alcohol, the random copolymer forms rhombic crystals (the same as polyethylene). Between these concentrations, a mixed crystal structure is formed. Only the monoclinic crystal structure is sufficiently dense to be used as barrier plastic.
U.S. Pat. No. 4,632,959 to Nagano concerns a dispersion of two different polymers in which one of the components can be an ethylene/vinyl alcohol random copolymer as illustrated in FIG. 1 of the present case, in which there are vinyl alcohol units between the ethylene units in a straight chain.
Polyvinyl alcohol (PVA) is principally used as a dispersing agent in PVC suspension polymerization. By regulating the molecular weight of PVA and its degree of hydrolyzation, the properties of the PVC can be regulated. When PVA has a sufficiently high degree of hydrolyzation, it is water-soluble. This water-solubility and difficult processability restrict the use of PVA in the plastics industry.
Dry PVA is noteworthy, because it possesses excellent barrier properties (gas-barriers). With a view to eliminating the drawbacks, the ethylene/vinyl alcohol random copolymer (EVAL) has been developed. However, the gas-barrier of EVAL is dependent upon moisture. It is therefore necessary to protect the EVAL film against air humidity, for example with a polyethylene film on both sides thereof. Moreover, EVAL does not adhere to polyethylene as is; an adhesion layer has to be additionally used between these components. It is however a fact that such a five-layer coextrusion design is highly exacting and expensive, with the EVAL and adhesion plastics similarly being very expensive.
EVAL may also be admixed with plastic, so that it is then less sensitive to moisture. For example, EVAL is admixed with polyethylene terephthalate (PET). In this manner, bottles with better gas-barriers can be produced, than by means of coextrusion. EVAL may also be admixed with polyolefins, whereby an adequate gas-barrier is obtained (a 30 to 50% addition of EVAL is equivalent to the resistance of polyamide). At the same time, adhesion to polyolefins is obtained (no adhesion plastic required) (Neste). The above-noted mixtures are macro-mixtures. Two phases are produced, and for this reason, the products are not transparent.
It is possible to produce silicone from silane by polycondensation. Silanes are used in the plastics industry as a coupling agent, as a cross-linking agent, and to improve adhesion. The coupling agent concept is based upon causing the hydroxy groups on the surface of a pigment or filler to condense with the silane. The chemical composition of the surface is thereby changed such that it wets the plastic, is admixed with the plastic, and/or conceivably reacts chemically with the plastic. Miscibility of the filler and plastic, the adhesion between the two, and the properties of both the molten and solid plastic mixture, are improved in this manner.
It is also possible to cross-link, for example, polyethylene with silane in a manner such that unsaturated alkoxysilane is grafted with the aid of peroxide or of electron radiation to the polyethylene chain. The silane groups are thereafter allowed to undergo hydrolysis, and to condense with the aid of water and a condensation catalyst. There is an abundance of patents and literature dealing with this technique. Grafting may also be achieved with silyl peroxide (Akzo), while the unsaturated silane may already be added as a comonomer at the polymerizing step (Mitsubishi). With silane, it is also possible to improve the adhesion, e.g. between plastic and metal, or between non-polar plastic and polar plastic in multi-layer products.